A certification exam wouldn’t survive a disparate impact challenge. Google stopped asking for SAT/ACT scores long before universities did. And long before that (according to my father, who actually used them), telegram companies had to stop giving spelling tests to telegraph operator applicants. Add to that difficulties with preventing cheating during a pandemic, and I see no alternative to rolling your own live examination. (Not that I’m defending the often dumb choice of trick tree recursion coding problems; I didn’t learn a lot about a candidate by watching him not get the trick.)

As an employer and not an academic institution, Google wasn't exactly visionary in ending requests for SAT/ACT scores, since virtually no other employer asks for them. Also, I interviewed w/ Google in ~2018, they still asked for my college transcripts even though I had been working in industry. So they still haven't fully shed their desire to academically successful people.

Just have the certification system be leetcoding on a whiteboard so the interviees need only pass it once rather than all the times for each FAANG, unicorn, and wannabe unicorn-FAANG startup that mandate such questions.

Other fields have certification exams. Why haven't they fallen to disparate impact challenges? Are you sure LeetCode would survive one?

Because just like how interviewing is gamed now by leetcoding, certification exams will also be gamed by some other phenomenon like 'certcoding'. There are plenty of certification programs floating around already, not to mention the coding bootcamps which behave something along those lines. Ultimately, it boils down to who plays the game better, be it interviewing process or certification exams.

At the very least, it would be nice if all the companies that want to use this standard could get together and design a certification that they all accept. If we could cut the length of interviews down by removing the leetcode portion it would save countless hours of both candidate and interviewer time.

+1 for some type of formal certification process.

Isn't a CS degree (from a non-degree-mill school) such certification process?

No, because computer science programs are not managed by a central authority, like the CPA or the CFA are, for example.